Unraveling mysteries of BAS wireless controls

There is quite a bit of flux in the wireless building instrumentation and controls protocol market with numerous players jockeying for dominance. Here’s a look at several of them.

By Sunondo Roy, PE, LEED BD+C, CCJM Engineers Ltd., Chicago

08/23/2012

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Whenever I am stymied on a particular technology related to building mechanical, electrical, plumbing (MEP), or fire protection design, I first check the various related master specification sections related to the subject. After that, I invariably troll the Web for noncommercial sites first and then vendor-specific sites to get as much information as I feel necessary to approach the design situation.

Back in the fall of 2010, my firm was moving its office, and we thought it was a great opportunity to test different emerging technologies. One of those technologies we had heard much about was wireless building automation. Our new office was an older building and we were maintaining much of the existing false ceilings as part of a U.S. Green Building Council LEED reuse credit. We decided to try wireless controls in various aspects of the design to minimize the amount of conduit in the ceilings and avoid disturbing the false ceiling as much as possible.

At the time, we did our usual research but didn’t find much by way of vendor-neutral documentation of wireless technologies. We figured that because the technology was relatively new, our various professional societies and standards organizations hadn’t caught up to the technology. In short order, we contacted some of our local sales reps to see what options we had and came up with a basic scheme to implement wireless lighting controls. We proceeded to implement an integrated lighting control scheme for the private and open offices. To summarize the effort, it appears to be a success in that the spaces with wireless lighting controls are working as seamlessly as the handful of spaces that remain equipped with wired lighting controls.

Figure 1 shows a sample open office application with ceiling-mounted occupancy sensors. The wall switch/transceiver is powered from building power while the ceiling-mounted occupancy sensor is powered by a lithium AA battery. Besides the cost savings of not installing the wiring and conduit between the sensor and the switch, the sensors were mounted with a removable adhesive pad that allowed repositioning the sensor to accommodate field-discovered obstructions.

This type of wireless installation is very well-suited for retrofit and historical preservation projects. With no new field wiring required, spaces can benefit from the immediate energy savings related to occupancy sensor controls and better temperature controls of optimally placed temperature sensors for constant volume or variable volume (VAV) systems. Many BAS vendors now offer wireless temperature sensors and local equipment level controllers with wireless routers that can collect and transmit signals to wireless sensors. Although the offerings for BAS integration are relatively slim, it is only a matter of time before other sensors such as humidity sensors, occupancy sensors, and even VAV and control valve actuators are added to the basic offering of temperature sensors. Once this happens, older installations where terminal devices were operating stand-alone can be effectively integrated into a cohesive BAS that can sequence and coordinate terminal devices throughout a building.

Specifying wireless products

For a small project, this approach of single-sourcing a vendor-recommended product is acceptable. However, for larger projects and those with multiple sourcing requirements, this approach won’t work and a formal specification will be required. Based on the dearth of information about wireless technologies, engineers will need to do their own research on wireless technology and write their own specification subsection within a standard instrumentation and controls specification.

The first task is to be knowledgeable of the design solutions that lend themselves to wireless technologies. The prevailing application of wireless technology in building automation is in the signal transmission of terminal control devices such as temperature sensors and binary actuators (on/off switches). Additionally, these same types of sensors can be located outdoors or in remote, hard-to-reach spaces or historic spaces where wiring and conduit would detract from the visual impression of the space or embedding or recessing wires and/or conduits is not an option. Beyond direct building automation, this technology also allows BAS integration with security systems, mobile devices, utility metering, building access, entertainment, and media devices.

An advanced application of this technology that uses the full capabilities of the underlying technology includes addressable controls of lighting and HVAC devices serving a space via these sensors from individual workstations at a master-controller level or even end-user level. Although this level of controls is currently possible with wired controllers and devices, the cost to run the wiring (typically in conduit) make the proposition cost prohibitive. Freeing up the signal transmission is the game changer. If lights and VAV boxes are tied into an office’s wide area network (WAN), it is a simple task to grant individuals permission to control these devices whether globally or down to personal comfort controls.

Know the protocols

The next task is to become familiar with the current available technology. At present, there are two wireless technology protocols that are all based on the IEEE 802.15.4 wireless standard, one on ISO/IEC 14543-3-10 and one on an unpublished, proprietary standard. The four protocols have very specific characteristics and target applications.

The most prevalent protocol in the United States at present is via the ZigBee Alliance, which is an open-source protocol based on IEEE 802.15.4 2011, IEEE Standard for Local and Metropolitan Area Networks—Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs), that operates in the 868–868.6 MHz, 902–928 MHz, and 2400–2483.5 MHz bands with in the U.S. It is the wireless protocol of choice of many of the major BAS and automation vendors such as Johnson Controls, Siemens, Trane, Philips, and Schneider Electric. To date, it has the widest brand awareness in the consulting engineering community. One of the major criticisms of this technology is that it resides in the crowed 2.4 GHz wireless spectrum, which also is used by Wi-Fi devices. Some literature on the IEEE standard indicates it is exploring expanding the wireless spectrum to other less crowded frequencies in the 300 MHz range.

The second protocol is called the EnOcean Alliance. It is a robust protocol based on ISO/IEC 14543-3-10, Information technology—Home Electronic Systems (HES)—Part 3-10: Wireless Short-Packet (WSP) protocol optimized for energy harvesting—Architecture and lower layer protocols, with the largest selection of sensor offering in the industry. Currently, its primary adoption has been in Europe with a relatively limited number of installations in the U.S. and Canada. It appears to be the only protocol that is set up to be not only wireless, but also battery-less. Most of the sensors and actuators have very small photo cells, piezoelectric switches, or thermoelectric converters that are capable of generating the minimal power required to transmit signals. The introduction of these battery-less sensors and actuators is a critical advantage in large commercial projects where building owners and managers may be reluctant to maintain Lithium-ion batteries for hundreds, and conceivably thousands, of sensors and actuators, even if the average life of the battery is 3 or more years. The protocol stresses using very low-power sensors and actuators with very small data packets that do not require much power to transmit.

The third protocol is called the Z-Wave Alliance and is geared toward the residential, hospitality, and light commercial market. It operates at nominal 900 MHz frequency and is also advertised as an open-source protocol for third-party developers of wireless applications.

The fourth protocol is called RedLINK and is developed and maintained by Honeywell. Like Z-Wave, it also operates at nominal 900 MHz frequency. This protocol is proprietary to Honeywell and it is unclear whether it follows the IEEE 802.15.4 standard.

Table 1 (below) provides a quick comparison of the four protocols and lists representative vendors supporting each protocol. When creating a customized instrumentation and controls specification geared toward wireless sensors, all technical data within the product section would generally be based on this data.

Courtesy: Comparison values are from the respective protocol websites.

The EnOcean protocol uses ISO/IEC 14543-3-10 as its underlying technology. IEEE 802.15.4 is the documented basis for ZigBee and Z-Wave. It is presumed that RedLINK also uses this standard, but it has not been confirmed. The fundamental system architecture inherent in IEEE 802.15.4 that allows this technology to transmit and receive control signals across a wide area is the concept of an ad-hoc mesh network. The communication network is based on the principle of a large number of low-power wireless transceivers on a decentralized peer-to-peer network.

According to IEEE 802.15.4—2011: These transceivers comprise a low rate wireless personal area network (LR-WPAN) that is a simple, low-cost communication network that allows wireless connectivity in applications with limited power and relaxed throughput requirements.1

Courtesy: Comparison values are from the respective protocol websites.

Two different device types can participate in a LR-WPAN network: a full-function device (FFD) and a reduced-function device (RFD). A FFD is a device that is capable of serving as a personal area network (PAN) coordinator or a coordinator. A RFD is a device that is not capable of serving as either a PAN coordinator or a coordinator. An RFD is intended for applications that are extremely simple, such as a light switch or a passive infrared sensor. 1

Depending on the application requirements, an IEEE 802.15.4 LR-WPAN operates in either of two topologies: the star topology or the peer-to-peer topology (mesh network). Both are shown in Figure 2. In the star topology, the communication is established between devices and a single central controller, called the personal area network (PAN) coordinator. A device typically has some associated application and is either the initiation point or the termination point for network communications. A PAN coordinator can also have a specific application, but it can be used to initiate, terminate, or route communication around the network. The PAN coordinator is the primary controller of the PAN. All devices operating on a network of either topology have unique addresses, referred to as extended addresses. A device will use either the extended address for direct communication within the PAN or the short address that was allocated by the PAN coordinator when the device associated. The PAN coordinator will often be mains powered, while the devices will most likely be battery powered. Applications that benefit from a star topology include home automation, personal computer (PC) peripherals, games, and personal health care. 1

The peer-to-peer topology also has a PAN coordinator; however, it differs from the star topology in that any device is able to communicate with any other device as long as they are in range of one another. Peer-to-peer topology allows more complex network formations to be implemented, such as mesh networking topology. Applications such as industrial control and monitoring, wireless sensor networks, asset and inventory tracking, intelligent agriculture, and security would benefit from such a network topology. A peer-to-peer network allows multiple hops to route messages from any device to any other device on the network. 1 The mesh network allows signals to “get around” obstacles such as dense wall construction or multi-story environments. The architecture is very stable because there is no rigid pathway for signals to travel. If a given node fails, there are numerous other nodes in the vicinity that can pick up the signal and continue its propagation around the network.

The LR-WPAN operates on one of three possible unlicensed frequency bands:

902-928 MHz: North America, up to 10 channels (2003), extended to 30 (2006)

2400-2483.5 MHz: worldwide use, up to 16 channels (2003, 2006) 1

The original 2003 version of the standard specifies two physical layers based on direct sequence spread spectrum (DSSS) techniques: one working in the 868/915 MHz bands with transfer rates of 20 and 40 kbit/s, and one in the 2,450 MHz band with a rate of 250 kbit/s. 1

The 2006 revision improves the maximum data rates of the 868/915 MHz bands, bringing them up to support 100 and 250 kbit/s as well. Moreover, it goes on to define four physical layers depending on the modulation method used. Three of them preserve the DSSS approach: in the 868/915 MHz bands, using either binary or offset quadrature phase shift keying (the second of which is optional); in the 2450 MHz band, using the latter. An alternative, optional 868/915 MHz layer is defined using a combination of binary keying and amplitude shift keying (thus based on parallel, not sequential spread spectrum, PSSS). Dynamic switching between supported 868/915 MHz PHYs is possible. 1

Writing project specs

With basic understanding of the wireless technology in building automation, the next step is to adapt the typical guide specification version of Master Format 23 09 00—Instrumentation and Control for HVAC or Division 25 equivalent for integrated automation systems to include wireless controls. The approach should be to incorporate the changes to supplement the existing specification with the basic information a contractor will need to know to incorporate wireless controls into standard building automation.

In order to do this correctly, it is necessary to understand the various aspects of a master specification than will need to be modified. At a minimum, the engineer will need to edit the Part 1 paragraphs summary, definition, submittals, and quality assurance. Under Part 2, a new product subsection will be needed for the wireless technology for control devices. By decoupling the wireless technology from the control devices, the engineer doesn’t need to get bogged down re-editing countless control devices.

Under summary, the first paragraph should be modified to read “This Section includes wired and wireless control equipment for HVAC systems and components, including control components for terminal heating and cooling units not supplied with factory-wired controls.”

Under definitions, it is recommended to provide an extensive list of terminology from the IEEE 802.15.4 and ISO/IEC 14543-3-10 standards which are not standard usage in the architectural engineering community. These include WPS, LR-WPAN, RFD, FFD, PAN, and any others that are referenced in the specification edits to include wireless controls.

Under submittals, add the following paragraph, “Data Communications Protocol Certificates: Certify that each proposed DDC system wireless component complies with IEEE Standard 802.15.4-2011 or current issue.” If the EnOcean protocol is used, reference needs to be made to ISO/IEC 14543-3-10 for compliance certification.

Under quality assurance, add the following paragraph “Comply with [IEEE 802.15.4] [ISO/IEC 14543-3-10] for wireless DDC system components.” If the EnOcean or RedLINK protocols are used, additional investigation is required to determine the applicable technology standard to reference for compliance.

Under Part 2, products, the following paragraphs should be included, as applicable to the project conditions:

Wireless Technology Protocol

A. Description: The following technology protocol shall be applied to wireless control sensors. B. Wireless Protocol:

The limited information available for each of the protocols can limit how much detail can be included in the specification. EnOcean does provide a guide specification formatted along the lines of standard guide specifications, but it only lists the technical criteria for its technology. As such, the specifying engineer is still left to his or her own devices to create a nonproprietary specification that allows multiple technologies to compete for a project. It seems greater coordination is required between the protocol developers and the specification writing organizations to bring greater transparency in the technology before a true master guide specification is developed.

At present, most developers are releasing the least amount of information possible to the general engineering community in order to guard their technology niche against competing protocol. Additionally, due to the divergent nature of the underlying technology and varying features of each of the protocol, there is limited ability to achieve meaningful competition between the various protocols on a given project. For now, the engineer and client will have to choose one protocol based on direct experience, protocol vendor sensor and switch offerings, and marketing literature and write the specification around the technology of that protocol. There is significant variety from multiple vendors within a protocol to achieve competitive bids, but not cross-protocol.

The engineer also will have to research and edit the acceptable manufacturers for specific sensors, actuators, and switches based on whether to the project is wired or wireless. For wireless sensors, actuators, and switches, the engineer may consider an additional entry within the standard wired performance criteria indicating the device is intended to be wireless and reference the wireless criteria. Additionally, the engineer may consider including a system architecture diagram to illustrate his or her design intent and clarify the extent of wired and wireless control devices to facilitate bidding, shop drawings, and ultimately, commissioning of the installed project.

There is quite a bit of flux in the nascent wireless building instrumentation and controls protocol market with numerous players jockeying for dominance. It seems until one or more of the protocol developers achieve a significant market dominance and provide guidance to establish vendor neutral specifications, there will be little chance that architectural engineering firms can reasonably expect to incorporate wireless technologies into larger competitively bid projects. The sooner the protocol developers realize this barrier to specifying their products, the sooner the technology can be broadly adopted within the building construction industry.

Roy is vice president with CCJM Engineers. He is a cross-disciplinary mechanical engineer who has successfully designed integrated mechanical/electrical systems for LEED-certified schools, as well as commercial, aviation, industrial, and institutional facilities for the past 24 years.